There is a continuing demand in industry for an alloy having the combination of high hardness and high electrical conductivity. These two properties are incongruous, since good conductivity is a property of pure metals, whereas high hardness is normally achieved by alloying the pure metal with one or more alloying elements.
Age or precipitation hardened copper-base alloys are well known. U.S. Pat. No. 1,658,186 discloses the precipitation hardening phenomenon in copper base alloys. More specifically, U.S. Pat. No. 1,685,186 describes a copper alloy containing silicon and one or more of a group of silicide forming elements, such as chromium, cobalt and nickel. The improved hardness is achieved by a heat treatment consisting of heating the alloy to a solution temperature, subsequently quenching the alloy to hold the bulk of the alloying elements in solid solution and thereafter aging the alloy to precipitate metallic silicides, resulting in an increase of hardness and an improvement in electrical conductivity.
U.S. Pat. No. 4,260,435 describes a precipitation hardened, copper base alloy, that is an improvement to the alloy described in U.S. Pat. No. 1,658,186. The alloy is composed of 2.0% to 3.0% nickel and/or cobalt, 0.4% to 0.8% silicon, 0.1% to 0.5% chromium, and the balance copper. The silicon, as disclosed in U.S. Pat. No. 4,260,435, is used in an amount slightly in excess of the stoichiometric amount necessary to form silicides of the nickel, thereby removing the nickel from solution and leaving excess silicon. The chromium is used in an amount slightly greater than the amount required to form chromium silicide with the excess silicon. Because of the low solubility of chromium in copper, the excess chromium will be precipitated by a second aging treatment.
With the double aging treatment, along with the chemistry, as set forth in U.S. Pat. No. 4,260,435, a heat treated alloy is obtained having a high hardness above 90 Rockwell B, along with a high electrical conductivity of over 45% of pure copper.
Copper-base alloys have desirable properties for use as components in blow molding dies, injection molding dies, reinforced composite dies or extruding dies for the plastic industry. Copper base alloys have lower machining costs, and offer excellent diffusivity, assuring better heat equalization of the die and reducing post die shrinkage and core warpage. However, there has been a need for a beryllium-free, copper-base die alloy hving a higher hardness, above 30 Rockwell C, while maintaining good electrical conductivity.